Local drag reduction due to injection of polymer solutions into turbulent flow in a pipe. Part II: Laser‐doppler measurements of turbulent structure

Abstract

a pipe flow through either a small tube at the center line or an annular slot in the wall. The solution contained polymer at an injection concentration of 1, OOO wppm. Injection into water flow with a Reynolds number Re = 3.5 X lo4 was at a rate which gave a mean polymer concentration of 5.0 wppm in the water flow. A laser-Doppler anemometer (LDA) was used to measure the streamwise turbulent velocity at various radial positions and at several stations downstream from the injection point.Results were obtained for mean velocity and intensity profiles; autocorrelations; and one-dimensional energy spectra. The mean bursting period was determined using the "short-sampling-time" autocorrelation method. Changes in all these quantities due to polymer injection were found to depend on the amount of local drag reduction at that particular downstream station but were independent of the local polymer concentration at the measuring point.

Heterogeneous drag reduction in turbulent pipe flows using various injection techniques

“…Investigations of Wells and Spangler [29] and McComb and Rabie [22,30] confirmed the hypothesis that the drag reducing macromolecules affect the near-wall region of the pipe flow. The centre-line injection of dilute polymer solutions leads to a drag reducing effect only when the macromolecules have been transported into the near-wall region by turbulent diffusion.…”

Developments in the Flow of Complex Fluids in Tubes

“…Thus, the additives have a direct effect on the flow processes in the buffer region, and the linear sublayer appears to have a passive role in the interaction of the inner and outer portions of the turbulent wall layer. The work of McComb and Rabie [56,57] is in general support of these findings as are the experimental results of Usui et al [58]. The work of the latter authors, who measured turbulent characteristics of drag-reducing flow by laser Doppler velocimetry (LDV), suggests that polymer (aqueous solutions of polyethylene oxide) injection into a pipe flow caused a thickening of the buffer layer, enlargement of macroscale turbulent eddies, and suppression of fine-scale turbulent eddies.…”

Turbulent drag reduction by polymer additives: Fundamentals and recent advances

“…Availability of detailed polymer conformation (and, consequently, stress) field information, thanks to extensive DNS efforts in the past two decades, has provided direct evidence in this regard. Earlier experiments have shown, by injecting polymers to different wall positions, that DR becomes substantial when polymers reach the near-wall region cover-ing the buffer layer and lower log-law layer 103,104 . The buffer layer is also where turbulence production peaks in Newtonian flow and where significant reduction in RSS is observed when drag-reducing polymers are added.…”